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I have an observation and a concern about my RV.

1) I installed a Tire Pressure Monitoring System in it, but only on the rear tires (it's a dually, obviously) because it only has 4 sensors.  I set the tires to 65PSI as I think it the generally-accepted suggestion here, but I notice that as I drive it, the pressure increases.  I set a low PSI parameter on the TPMS of 50PSI and a high of 75PSI, thinking that it would never get that high.  I'm finding that my pressure, in what I consider to be normal conditions (judicious driving, 65-85 degree ambient temperature, 60-65MPH), the pressures quickly rise to 70PSI.  And then, if with some warmer driving (85-95 degrees), they go to 75PSI and trigger my high-pressure alarm.  I can't help but think that some higher temperatures (say like driving in Arizona in 100-105 degrees) would cause my tires to quickly exceed 80PSI and I consider that dangerous pressures.  Or am I crazy?  Thoughts?  Of course, my concern is a blowout.

2) I'm having to fill up this "5-gallon" propane tank quite frequently.  It gets down to 1/4 or just a hair less, but when I have it filled, they can never get more than 2 - 2.5 gallons in there.  One guy told me that the actual capacity of this tank is actually closer to 3 - 3.5 gallons.  It's a new tank, but it looks to be the exact same size as the one that was there, and fits the exact same spot.  Question is - do I have a 3-gallon or a 5-gallon LP tank?

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" I set the tires to 65PSI as I think it the generally-accepted suggestion here ...".

I can't agree with that. Others might. My usual suggestion is to start at 50psi and then adjust gradually until you find a balance of ride, handling, braking and economy that suits you.

Here's what National RV (Dolphin) actually posted:-

1993 Dolphin 36 45psi.jpg

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1 hour ago, Derek up North said:

My usual suggestion is to start at 50psi and then adjust gradually until you find a balance of ride, handling, braking and economy that suits you.

I did exactly this process per suggestions from this forum and I ended up with 55 in the rears and 50 in the fronts.  This is measuring cold.  I have also noticed pressure increasing after driving for a while but I see only about 10 psi increase.  I found that at 65 psi (cold) the ride was noticeably rougher.

9 hours ago, lopezg273 said:

2) I'm having to fill up this "5-gallon" propane tank quite frequently.  It gets down to 1/4 or just a hair less, but when I have it filled, they can never get more than 2 - 2.5 gallons in there.

I have a  horizontal 5 gallon tank and I typically get 3.5 to 4 gallons into it if the gauge goes down to 1/4.  

The gauges on these tanks are not super accurate and the pressure to volume change is non-linear -  which shows on the gauge itself as the needle swing is not the same for 1/4 to 1/2 as it is for 3/4 to full.   Maybe the gauge is just off?  Maybe it's more than 1/4 full when the gauge says 1/4.  Or maybe they are not filling it up to full pressure?  I forget if the "full" pressure is determined by a gauge/valve on the tank itself or on the fill hose.   Others with more actual propane tank knowledge will probably have a better idea of what's going on than me.

If you really want to know your capacity you can do a few rough measurements and a calculation to estimate gallon capacity.

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What is your propane tank? There are different types. A 20#  horizontal RV tank will hold about 4.7 gallons it's valve if it's new will be close to the top. A 20# BBQ tank can not be used on its side and is not designed for RV use it's valve will be in the center. If the tank is mounted to the frame it is a 30# tank. 

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6 hours ago, Derek up North said:

" I set the tires to 65PSI as I think it the generally-accepted suggestion here ...".

I can't agree with that. Others might. My usual suggestion is to start at 50psi and then adjust gradually until you find a balance of ride, handling, braking and economy that suits you.

Here's what National RV (Dolphin) actually posted:-

1993 Dolphin 36 45psi.jpg

I should have mentioned that I have ONLY the rears at 65PSI.  The front I have at 55PSI.  I also have Airlift Airbags in the rear, at around 50PSI.  This seems to work fine, but I've been driving around the SFO and LAX areas (especially SFO) and I find that there are a lot of expansion joints which I find jarring.  I'm also averaging around 15MPG.  I think I'll try 50PSI on the fronts to soften up the expansion joints and lower the rears to 55PSI and see the effect on ride and MPG.  And then play around depending on what happens.  Thanks!

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I'll add the new tanks will automatically shut off when being filled they have a float inside that will not allow them to be overfilled but it still should  be able to hold their rated amount. Liquid propane is 4.2 LBS per gallon

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I used to be anal about inflating duallys to the exact same pressure. Almost bought a dual head inflator so both tires would be the same.   Then I got a 4 tire pressure monitor and found that the pressures are all over the chart, the tire in the sun vs the one that is shaded can be way higher!  The tires on the shaded side are always lower psi than the ones in the sun.

The monitor did alert me of a leaking inner dual on a trip, which I would not have noticed, so maybe saved me a tire?   

Cheap monitor system lasted me about a year.

65 psi may be generally accepted somewhere but not on my Toy.   Tire place put 65 psi in mine and on the way home thought I was going to jar my teeth loose or hurt my back,  like riding on bowling balls! 

https://www.youtube.com/watch?v=d-gPwNZgDGA

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